1. Field of the Invention
The present invention relates to a spread illuminating apparatus.
2. Description of the Related Art
Along with the high performance of recent blue light-emitting diodes (LED), a spread illuminating apparatus, to which LEDs are applied as a light source, has been widely used not only for the backlight of a large flat-screen television but also for the lighting device of an indoor lighting.
A generally known structure of the spread illuminating apparatus is a so-called sidelight type. This type includes a light guiding plate that forms a light emitting surface, LEDs that are arranged to face a side end face of the light guiding plate, and a circuit board on which the LEDs are mounted. FIG. 4 schematically illustrates this type of spread illuminating apparatus. The basic structure of a sidelight type spread illuminating apparatus 100 includes a light guiding plate 101, a plurality of LEDs 102 that are arranged to face a side end face (light incident surface) 101c of the light guiding plate 101, and a circuit board 104 on which the LEDs 102 are mounted, the circuit board 104 facing the light incident surface 101c of the light guiding plate 101. The light guiding plate 101 is a plate-like light guiding body which is made of a transparent resin material such as methacrylic resin or polycarbonate resin. In FIG. 4, an emission surface 101a, which is one principal surface of the light guiding plate 101, is provided with triangular prisms of the same shape in which to be arranged at equal intervals, each extending in a direction orthogonal to the light incident surface 101c. A reflection surface 101b, which is the other principal surface facing the emission surface 101a, is provided with a diffuse reflection means or a specular reflection means, either means being adapted to reflect light that has been incident on the reflection surface 101b. Accordingly, at least a part of the reflected light is introduced into the emission surface 101a at an incidence angle equal to or smaller than a critical angle.
In FIG. 4, a prism sheet 103 is disposed over the emission surface 101a of the light guiding plate 101. The prism sheet 103 is a sheet member made of a transparent resin material such as a PET film. At a principal surface 103a of the prism sheet 103, triangular prisms are provided with multiple rows extending in one direction, the prisms being made of a methacrylic resin or a polycarbonate resin. The principal surface 103a of the prism sheet 103 is disposed to face the emission surface 101a of the light guiding plate 101. Accordingly, the extension direction of prisms on the prism sheet 103 will be orthogonal to the extension direction of prisms of the light guiding plate 101.
Here, although not illustrated in FIG. 4, a reflection plate may be provided to the LED 102, or to a portion just below the light guiding plate 101. Further, it has been generally known that the sidelight type spread illuminating apparatus is integrally configurable into a single unit with a frame by enclosing components therein (refer to Japanese Patent Application Laid-Open No. 2006-286347).
When the sidelight type spread illuminating apparatus is applied as the backlight of light flat-screen televisions or lighting devices for indoor lighting, the plurality of LEDs needs to be arranged along the light incident surface 101c of the relatively large sized light guiding plate 101 in order to achieve sufficient luminance properties needed. Thus, the circuit board 104, on which the LEDs 102 are mounted, should be necessarily sizable. However, it is practically difficult to make the circuit board 104 large enough to correspond to the size of the light guiding plate 101 due to restriction factors such as an LED mounting apparatus or an available reflow size. Accordingly, at present, for the circuit board to be applied to large-sized spread illuminating apparatuses, a number of circuit boards, each manufacturable by present or conventional manufacturing devices, will be typically connected to each other.
However, when existing connectors are used as a connecting means of the circuit boards, available connectors are to be narrowed in handling of other components. Accordingly, some types of the circuit boards may not be connected with the existing connectors. There is an alternative method which uses wire rather than using the connector for connecting the circuit boards. However, connection works without using the connector will be further complicated.